securely overwrite files with Python
Skip Montanaro
skip at pobox.com
Fri Mar 5 17:54:44 EST 2004
>> First: It is not possible. Let me cite some sentences from shred(1):
>>
>> CAUTION: Note that shred relies on a very important assumption: that
>> the filesystem overwrites data in place. This is the traditional way
>> to do things, but many modern filesystem designs do not satisfy this
>> assumption.
Bob> Somewhat OT, Mac OS X 10.3 is one of the operating systems where
Bob> this assumption is false. Files smaller than a certain size get
Bob> automatically moved around on the disk when it makes sense to do so
Bob> in order to reduce fragmentation.
I'm not sure I understand how that can work. Suppose I have multiple (hard)
links to a small file named "small". If the OS moves it around to reduce
fragmentation (implying it will have a different inode next time it's
opened) how does it efficiently track down and change all inode references
to it? In theory it could keep a cache mapping inode numbers back to the
directories which reference them, but that could consume a fairly large
chunk of memory to maintain.
Skip
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